USMC Machine Guns and Machine Gun Gunnery Flashcards

Comprehensive vocabulary flashcards covering weapon classifications, characteristics of fire, direct and indirect lay techniques, fire control, computed gunnery, and employment principles from MCTP 3-01C.

Light Machine Gun

An automatic weapon generally classified in $.22$ to $.250$ caliber ($5.45\,mm$ to $6\,mm$), weighing between $15$ and $30\,pounds$ complete, manned by one or two individuals, with bullets weighing between $45$ and $72\,grains$.

Medium Machine Gun

An automatic weapon generally classified in $.264$ to $.33$ caliber ($6.5\,mm$ to $8\,mm$), weighing approximately $25\,pounds$ or more by itself, manned by a standard crew of three, firing bullets weighing between $140$ and $220\,grains$.

Heavy Machine Gun (HMG)

An automatic weapon classified in $.50$ caliber or larger ($12.7\,mm$ to $21\,mm$), weighing over $125\,pounds$ without ammunition, firing bullets weighing $700\,grains$ or more, and manned by a crew of four or more.

Grenade Machine Gun

A type of heavy machine gun designed to fire an explosive grenade projectile (typically $30\,mm$ to $40\,mm$) from an open-bolt position at a relatively low muzzle velocity, not requiring a quick-change barrel due to its slow rate of fire.

Automatic Rifle

An automatic weapon featuring a fixed barrel that fires from a detachable box magazine, is manned by a single rifleman, and is designed for short-term missions against point targets rather than sustained automatic fire.

Gas Operation

An automatic weapon operational design in which the cycle of functioning is driven by diverting propellant exhaust gases from the barrel into a cylinder to drive a piston mechanically connected to the bolt.

Recoil Operation

An automatic weapon operational design driven by recoil forces, where the barrel and bolt recoil locked together for a portion of the recoil phase before unlocking.

Blowback Operation

An automatic weapon operational design in which the bolt is driven rearward solely by the pressure generated by expanding propellant gases against the cartridge case, without mechanical locking of the bolt.

Trajectory

The vertically curved flight path taken by a bullet after leaving the muzzle of a gun, influenced by gravity, air resistance, bullet weight, velocity, and rotation.

Bullet Drift

The rightward deviation of a projectile from the axis of the bore at longer ranges, caused by clockwise rotation imparted by barrel rifling.

Maximum Ordinate

The highest point above the line of sight (LOS) that a projectile reaches along its trajectory, occurring at approximately one-half to two-thirds of the distance to the target.

Battlesight Range

A sight setting for an optic or mechanical sight that allows effective engagement from zero out to a determined range without altering hold or sight settings.

Maximum Usable Range

The distance visible to the leader or gunner based on terrain and vegetation, strictly within the maximum effective range of the weapon when employed in direct lay.

Burst of Fire

A series of successive rounds fired with a single elevation and point of aim when the trigger is continually depressed.

Sustained Rate of Fire

The firing rate that a machine gun can deliver indefinitely without causing a malfunction due to weapon overheating.

Rapid Rate of Fire

The firing rate delivered for a short duration without overheating malfunctions, requiring more frequent barrel changes.

Cyclic Rate of Fire

The maximum continuous rate of fire of a weapon system, determined strictly by its mechanical design and ammunition.

Cone of Fire

The group of slightly differing trajectories resulting from a burst of fire due to gun vibration, tripod movement, atmospheric variations, and ammunition differences.

Beaten Zone

The cigar- or oval-shaped pattern formed on the ground where the trajectories within the cone of fire strike the surface.

Center of Impact

The center of the beaten zone, containing approximately $82\%$ of the rounds in a burst uniformly grouped to form the effective beaten zone.

Danger Space

The area from the muzzle out to and including the beaten zone where a standing person ($1.8\,m$ or $70\,inches$ tall) will be hit by some portion of the cone of fire.

Dead Space

An area within the maximum range of a weapon that cannot be covered by fire or observation due to intervening obstacles, ground contours, or trajectory limits.

Grazing Fire

Fire in which the center of the cone of fire does not rise higher than $1\,meter$ above the ground surface.

Plunging Fire

Fire in which the danger space is confined strictly to the beaten zone because rounds strike the ground at an acute or steep angle.

Frontal Fire

Machine gun fire delivered directly against the front profile of a target.

Flanking Fire

Machine gun fire delivered against the side or flank profile of a target.

Oblique Fire

Fire delivered so that the long axis of the beaten zone forms an oblique angle relative to the long axis of the target formation.

Enfilade Fire

Fire delivered so that the long axis of the beaten zone coincides or nearly coincides with the long axis of the target formation.

Fixed Fire

Fire delivered against a single point target requiring little or no manipulation of the traversing and elevating mechanism.

Traversing Fire

Fire distributed horizontally across a shallow (wide) target by making successive directional changes using the traversing hand wheel.

Searching Fire

Fire distributed vertically across a deep (narrow) target by making successive elevation changes using the elevating hand wheel.

Traversing and Searching Fire

Fire distributed across width and depth simultaneously against an oblique target using minor adjustments in direction and elevation.

Swinging Traverse Fire

Fire delivered against wide troop formations or fast-moving targets requiring major lateral shifts without elevation changes, executed by unlocking the traversing slide lock lever.

Free Gun Fire

Fire delivered against fast-moving targets requiring rapid changes in direction and elevation, executed by completely disengaging the T&E mechanism from the traversing bar.

Mil

A unit of angular measurement equal to $1/6400$th of a circle, with approximately $17.8\,mils$ per degree.

Mil Ratio

The mathematical relationship where $1\,mil$ of angular measurement equals $1\,meter$ of lateral distance at a range of $1,000\,meters$.

WERM Formula

The mathematical formula expressed as $W = R \times M$, where $W$ represents lateral width in meters, $R$ represents range in thousands of meters, and $M$ represents angle in mils.

Direct Lay

The technique of fire in which the gunner aligns the weapon's sights directly on the target.

Indirect Lay

The technique of fire in which the weapon is laid such that the target cannot be seen directly from the gun position, requiring alternative aiming methods.

Final Protective Line (FPL)

A predetermined line of grazing machine gun fire designed to create an impenetrable barrier of fire to stop an enemy assault across friendly defensive lines.

Principal Direction of Fire (PDF)

A predetermined line of machine gun fire assigned to cover the primary or most dangerous avenue of approach into a defensive position.

Line of Sight (LOS)

The straight line extending from the gunner's eye through the rear sight aperture and front sight post to the target.

Line of Bore

The straight line extending through the center axis of the barrel from the chamber to the target.

Angle of Sight

The vertical angle formed between the line of sight and the horizontal plane.

Vertical Interval

The vertical difference in elevation (measured in meters) between the position of the gun and the position of the target.

Angle of Elevation

The angle formed between the line of sight and the central axis of the bore.

Quadrant Elevation

The vertical angle formed between the horizontal plane and the central axis of the bore, calculated as the algebraic sum of the angle of sight and angle of elevation.

Minimum Clearance

The prescribed vertical clearance distance required between the center of the cone of fire and the feet of friendly troops during overhead fire.

Safety Angle

The angular difference in mils between the angle of elevation required to hit friendly troops and the angle of elevation required to ensure minimum troop clearance.

Overhead Safety Limit

The point on the ground between the gun and target where the lower bound of the safety angle intersects the terrain.

Defilade Fire

The delivery of fire from a weapon position protected from hostile observation and direct fire by an intervening land mass or mask.

Parallel Sheaf

An arrangement of fire from multiple guns on identical azimuths, producing parallel, evenly spaced beaten zones.

Converged Sheaf

An arrangement of fire from multiple guns where individual directions are modified to cause beaten zones to overlap onto a concentrated area.

PICMDEEP

The mnemonic representing the eight principles of machine gun employment: Pairs, Interlocking fires, Coordination of fire, Mutual support, Defilade, Enfilade, Economy, and Protection.